1. Field of the Invention
This invention relates to a thermal protector protecting, against an overcurrent and/or an overheat, an electric motor enclosed in a hermetically sealed housing of an electrically-driven compressor, the housing further enclosing a compressing means and a predetermined amount of refrigerant gas, and more particularly to such a thermal protector of the type that it is disposed in the compressor housing.
2. Description of the Prior Art
Various types of thermal protectors comprising a bimetal or other thermally responsive switch elements driving a switch have conventionally been used for protecting an electric motor against an overheating condition due to overload in hermetic electrically-driven compressors. In one of the types, the thermal protector is disposed in a hermetically sealed housing of the compressor so that better heat exchange can be achieved between the thermally responsive switch and the motor or the refrigerant gas. In this type, the thermal protector is closely bound to coils of the motor with strings, as shown in FIGS. 1 and 2 of Japanese Unexamined Utility Model Application No. 55-87170. Furthermore, the thermal protector is mounted on an elastic member further mounted on an inner wall of the compressor housing, as shown in Japanese Unexamined Utility Model Application No. 60-95183.
Binding the thermal protector to the motor coils with the strings is not easy but rather troublesome. On the other hand, the mounting is rendered easier when the thermal protector is mounted on the elastic member in the compressor housing. In this case, however, the elastic member and other mounting parts need to be previously provided in the compressor housing. Furthermore, since an excessive space for insulation is required between the compressor housing and the motor windings, the compressor housing is rendered large-sized.
In view of the above-described disadvantages, U.S. Pat. No. 4,791,329 issued Dec. 13, 1988 discloses a motor protector to which terminals in the form of tabs or receptacles are secured. The protector is enclosed in a socket or mounted on an outer face of the socket. Then, the terminals of the motor protector are directly connected to terminal pins of a glass-insulated power-supply terminal disposed in the compressor housing.
The above-described motor protector is large in size although it is of a so-called plug-in type. Furthermore, its attachment to and detachment from the power supply terminal are not so easy as to be expected. Additionally, the manufacturing cost of the above motor protector is relatively high. In the above mounting structure, however, a force caused by vibration or the like during operation of the compressor acts on a secured portion between the protector and each terminal. Consequently, the secured portion between the protector and each terminal is distorted or bent. Thus, reliability in the mechanical strength of the secured portion is low.